The present invention relates to a lens-shutter type camera having a zoom imaging optical system, a finder optical system separate from said zoom imaging optical system, and an electronic flash defice, and specifically to a zoom finder for such a camera. More particularly, it relates to a zoom finder capable of effecting zooming with the eyesight through the finder being kept constant when it is used with a lens-shutter camera, a video camera or other types of cameras that are equipped with a zoom lens system.
The recent advance in technology for providing lens-shutter type cameras with a zooming capability has been remarkable, and versions having zoom ratios of 3 or more are presently available on the market. One of the problems that have occurred as a result of the efforts to increase the zoom ratio is how to insure the optical path length of the finder optical system. An albada finder which has been commonly used may be provided with a zooming capability, but this is difficult to accomplish if the zoom ratio exceeds a certain value. Although a real-image (Kepler type) finder seems to be the inevitable alternative, it requires a longer optical path than the albada finder because the real image of a subject formed with an objective lens must be inverted and reversed right and left by means of such elements as other lenses, a prism and a mirror for viewing after enlargement with an eyepiece system. This problem becomes substantial if a zooming capability is provided, because a longer optical path must be allowed for the movement of a zooming lens and since the length of the optical path increases with increasing zoom ratio.
Thus, a lens-shutter type camera that adopts a real-image zoom finder and which is designed to have a large zoom ratio is unable to insure the necessary optical path length with the traditional camera configuration, and this has given rise to the need for changing the configuration of the camera itself. In other words, it has become difficult to use the traditional camera configuration and design a real-image zoom finder having high zoom ratio.
On the other hand, cameras such as lens-shutter cameras and video cameras employ an imaging system and a finder system as mechanically separate components. If a zoom lens is to be used in the imaging system, it is desirable to employ a zoom finder the magnification of which varies in accordance with the degree of zooming and such a zoom finder is already available. Most of the zoom finders used today are classified either as reverse-Galilean finders of the type described in JP-A-53-63014 (the term "JP-A" as used herein means as "unexamined published Japanese patent application) or as real-image finders of the type described in JP-A-61-156018.
A reverse-Galilean finder is so designed as to view a virtual image formed with an objective lens, but it involves difficulty in increasing the finder magnification and zoom ratio. In addition, it suffers from the problem of an unclear finder frame. To avoid these problems, the use of a real-image finder capable of viewing a real image is desirable. However, a real-image finder has such a construction that its overall length will increase inevitably. The zoom finder described in JP-A-61-156018 is so designed that the first lens group has a negative power but the finder magnification must be reduced in order to shorten the overall length, or the zoom ratio cannot be increased without causing increased variations in the overall length upon zooming.
Recent versions of lens-shutter cameras and video cameras are characterized by the increasing use of zoom lenses with high zoom ratio in the imaging system but on the other hand, the size of camera body itself is becoming smaller. Thus, it is desired to install in these cameras a zoo finder that is compact and which is so constructed that a high zoom ratio can be easily attained without experiencing any substantial aberrational variations upon zooming.